Xotic - RC Booster V2

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
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turbofeedus
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Post by turbofeedus »

I've played these a few times and always liked them.
The usability is insanely bad, you have to have fairy fingers with the stock knobs in order to use the second gain knob. The stompswitches are way to close together.
Anyway, I found one used and picked it up. Was surprised to find mostly through hole components, and pretty well made. Not surprised at all to find a sanded IC. :roll:
I started to trace and to be honest with y'all, I got bored. I did find a few discrepancies with the RC booster schematic floating around though (this is V2 version).
Hopefully someone with more motivation and less depression will pick up the torch.

Photo album:

Discrepancies observed:
C1 & C2: 1uf
R5: 22K
first opamp stage uses "second" opamp in the package, rather than the first as shown in V1 schematic
feedback diodes are 1N4007, three in series, and symmetric.

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Last edited by turbofeedus on 02 Jun 2020, 06:04, edited 1 time in total.

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ch1
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Post by ch1 »

I also started to trace it from the pictures and was most interested in how the gain 2 knob works. But i couldn't see enough on the pictures to find out. I wonder if it just changes between two different pots or if some other somponents are added too?
Which schema do you refere to for c1, c2 and r5?

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modman
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Post by modman »

Hey, great contribution, I took the liberty of attaching the pictures.... I jacked up the max file size (but 4MB pictures...hmm) and with the new software you can now drag pictures into the message window. Some pictures got traced years later, but that only possible if the pics are there.
Fighting dead links on daily basis.

original RC Booster schematic
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turbofeedus
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Post by turbofeedus »

I figured big pictures would be beneficial. I can resample at max 1MB if that's better.

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karul
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Post by karul »

turbofeedus wrote: 10 Feb 2020, 00:37 I started to trace and to be honest with y'all, I got bored. I did find a few discrepancies with the RC booster schematic floating around though (this is V2 version).
Hopefully someone with more motivation and less depression will pick up the torch.
I've try to trace it, something is visible, something can be guessed. It seems that the schematic is the same as the one for the V1.

Some notes:
Q1, Q2 - BC849 (2CW smd)
Metal film resistors were used only for power supply bias network.
1u, 10u Nichicon MUSE ES series bipolar caps, and one 100n WIMA in audio path.
Cant confirm the values for the ceramic capacitors, I guess they are the same.
Gain 2 pot is wired in series with the gain 1 pot with switch in parallel, that turns it on/off.
12V zener back to back protection at the input and output of the pedal. There are two more transistors on the small board with the switches. I'm not sure about the markings (one is 6Y?) , I'm almost positive that they are some fets, part of the switching circuit.
Also there are two diodes for polarity protection, one in series (schottky 1N5817), one in parallel.

What is missing on the photos is the value for the gain 2 pot. Gain 1 is clearly visible and it's B250k. I guess there's no reason the bass and volume pots values to be changed, and they are still the same, B50k and B100k. Tone pot value is visible, B50k.

turbofeedus thanks for the photos. Can you tell what was the value for the second gain pot, the one with the transparent shaft?

Schematic is already drawn I'm only missing the gain pot value.
Attachments
gain pots.webp

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